An interesting essay, as usual. But I think Michael meant Panasonic 35-100mm, rather than 200mm as the lens he used with the OM-D E-M1.Regarding the assertion that the new small Sony's will become a major market force when lenses are available, I think that's true for primes. But zooms equivalent to the above mentioned Panasonic will still be large and heavy. So for zoom users like me, the M43 kit will still have considerable appeal.

Though people make a big deal about shallow dof I often find myself stuggling for more depth of field and needing to bump the iso than the reverse. Often I wonder if I may well be served with a smaller sensor.

It doesn't matter how small Sony's mirrorless bodies are, high performance full frame lenses are larger for a given maximum aperture. It's not the weight of the camera body that got me into a Micro Four Thirds system to complement my full frame system. The real difference is the lenses.

While I have fast, compact f/2.8 zooms for my MFT system they do not equal my full frame "equivalent" zooms. Discounting the poorer image performance of the MFT sensor, the MFT lenses would need to be two stops faster to provide the same creative depth of field capability. Landscape photographers typically look for more DOF, so there are some benefits that come from the smaller format.

Discounting the poorer image performance of the MFT sensor, the MFT lenses would need to be two stops faster to provide the same creative depth of field capability.

less than two stops, because imaging area of FT/MFT sensors are not 4 times less than 24x36mm (that is if you believe that 24mmx36mm is actually the area from which the image data is written to raw files and not just the sensor size), but 3.7 times or better.

The argument of smaller size and weight made me do a little calculation between using a Sony A7 and a Canon 6D with two zoom lenses. Sony A7, 474g, 24-70 f/4, 426g, 70-200 f/4, 840g and Canon 6D, 770g, 24-70 f/4, 600g, 70-200 f/4, 756g. Sony total 1740g and Canon 2126g. So the Canon weighs 386 g more or 22%. If we did the same calculation for Fuji with the X-Pro1, 18-55 and 55-200 zooms, the total weight would go to 1360g and loose a little on the wide angle side.

So to me it seems as a small difference which might be possible to shrink further on the DSLR side. The main thing is f/4 lenses. On the Canon side f/2.8 lenses would add 1kg. The Fuji set is again 400g less.

Regarding resolution, the questions is, as Michael writes, how much do you need? The Sony A7 and the Canon 6D are very close to each other in resolution and probably also with the lenses mentioned. Obviously there are no DxO measurements to check, but test images from http://www.imaging-resource.com/ clearly shows that the detail from the Canon 6d is considerably better than the Fuji X-Pro1. The test scene is this one http://www.imaging-resource.com/camera-reviews/sony/a7/AA7hSLI00100NR0.ARW.HTM as a RAW file. The A7 resolves a little more than the 6D in the test. The performance of the 24-70 lens from Sony is unknown at this point.

Larger sensors give higher resolution, better dynamic range and less noise for the same output size which can be seen via DxO measurements (although m43 and Fuji are missing for lens and camera body measurements).

Yes, Sony will stir up the market with the A7(R) but the difference in size and weight for a system is not as large as one might think. We are still waiting for the fast PDAF in the mirrorless bodies to implemented such that the mirrorbox in DSLR's can be made redundant. However the reduction in size and weight on a system level is not huge but welcome.

An interesting essay, as usual. But I think Michael meant Panasonic 35-100mm, rather than 200mm as the lens he used with the OM-D E-M1.Regarding the assertion that the new small Sony's will become a major market force when lenses are available, I think that's true for primes. But zooms equivalent to the above mentioned Panasonic will still be large and heavy. So for zoom users like me, the M43 kit will still have considerable appeal.

An interesting and well thought post, as usual for Michael. If full frame (24x36 mm) is no longer needed for most purposes, what does this say about MFDB (medium format digital backs)? Probably overkill for all but the most demanding applications.

This photo says it all for me. For prints up to 24 inches wide the IQ of the Fuji is no worse and is in some respects better than the 5DII, and certainly better than the 7D shown here. But at around 2.5 kg versus 4.5kg, there's not a lot to dislike. I am tired of getting heavy kit onto planes.

What is "needed" for the amateur (such as moi) is very personal. If I were shooting for the web or publication m4/3 would be a no-brainer, but I'm not. I can't tell the difference between 17x22 prints on the wall from D800E and E-M5. But I can from 6", and that keeps me lugging the Nikon around instead of the Oly even though it's a lot bigger and weighs a full 2 pounds more (with their respective lenses). To me, the A7r with the Zeiss zoom looks a lot like the best of both worlds, I'm looking forward to renting it for a couple days when the zoom is available. It's a question of whatever floats your particular boat.

My fully loaded camera bag weights north of 30 LBS, my working kit for ten days, including the camera bag, weights north off 100 LBS shaving a few pounds of doesn't interest me much, I do big prints, and I do crop, so I guess I'm stuck, but in a good way!

I do enjoy the Sigma DP Merrills (APS-C), particularly for lightweight hiking kit with monopod or lightweight tripod. The DP Merrills weigh ~ 500 g each with permanently attached L bracket/ grip, versus 1.5 kg for APS-C DSLR and 15-85mm f/3.5-5.6 lens, my other hiking kit. I grab ONE DPM when I head out the door for a conditioning hike, and either a monopod or a tripod (additional 0.75 to 1.5 kg) - my water bottles weigh more! I suppose that there still is some advantage to having view camera style movements for some uses, and most of the time that has meant MFDBs.

On the other hand, I want to go on a birding long weekend in early spring (Nebraska), and need to start pumping iron so I can hand hold the rented 4 kg supertelephoto lens....

Ya know, after a year of shooting with the D800, there is no doubt that I don't need that many mp for what sizes I print. The crop factor is something I appreciate, though. I tried an NEX-7 and quickly discarded it because of the interface and the quirky nature of the EVF. I won't ditch my Nikon but I probably will do more shooting with my Leicas. While I like the size factor of the Sony's, I am not convinced they have their act together. I recently tried a Zeiss Otus, but what's the point when I only print to 24" on the short end? OTOH, isn't this a great time to be a photographer, with all these high quality choices. Yummy.

Like Michael, I have a D-800 system with a range of lenses, and an m4/3 (Panasonic) system with a range of lenses; and for the same reasons. When I'm working out of my SUV, I take the Big Trombone, and a suitcase full of lenses. Why not? Otherwise, it's the m4/3. But as for the future of the systems, I somewhat disagree with the article. As he says, the A7 cameras are in fact the size of some m4/3 cameras -- almost identical in size to the Panasonic GH3. But the GH3 is the largest of the m4/3 cameras, because it's basically a movie camera, and has to meet some movie camera requirements. I had one for a while, because I liked the sensor, but it was too big; not enough difference between it and APS-C cameras, so my son now has it. The future of the m4/3 still-camera systems, I believe, lies in the smaller bodies like the GX7, which are notably smaller than the A7 cameras (or the GH3.) I'd agree that small lenses are coming for the A7, and why not, if Leica can do it? But the thing is, I don't believe people really want those small Leica-style lenses...because the small lenses that are coming aren't zooms, just as the small Leica lenses aren't zooms. And I think people really want zooms -- and the enthusiasts want fast zooms. When I'm traveling by air, as I did this morning between LA and Santa Fe, I take my m4/3 system in two small padded Eagle Creek cases, not specifically meant for cameras, and I carry them in a business-style backpack. My basic kit includes 2 f2.8 zooms, (12-35 and 35-100) plus an f4 7-14, an Olympus 45mm and the Voightlander f0.95 42.5mm, a battery charger, and two spare batteries. Sometimes, I'll drop an extra GX7 body in the bag. Not bad, for a system that shares a fairly small pack with a Surface tablet, pens, pencils, books, chargers, spare glasses, sun glasses, pills, etc. That system is *smaller* that two of my Nikon f2.8 zooms alone. In my opinion, in a situation where cost is not a major factor, the *only* real reason for carrying a system smaller than FF is size and convenience..I'd never argue that the image quality is as good, or that the systems are more photographically flexible. But if you're going to go small, I would suggest that you want to go as small as you can, and still meet your IQ requirements, whatever they may be. The m4/3, for me, meets my IQ requirements for the kind of shooting I use it for -- otherwise, it's the Big Trombone.

I should also mention the epitaph I plan to have inscribed on my tombstone, which I feel is relevant here: "No great photograph ever depended on resolution."

I can't tell the difference between 17x22 prints on the wall from D800E and E-M5. But I can from 6", and that keeps me lugging the Nikon around instead of the Oly ...

Yes, you can look at a image from 6", or even with a loupe. But to me that's not really looking at an image, it's looking at pixels. With that, bigger sensor is always better.

But photography is about much more. It's the light, the idea, the composition, the subject. Most of the time, I couldn't get these things right. Having slightly better resolution and dynamic range really doesn't help me that much unfortunately. But having a small, easy to handle system with super fast focusing can sometimes increase my odds of taking better photos. That's how I ended up ditching all my Canon gears and getting into the M43 system.